Chiral fourth-generation quarks, or , with identical properties to the SM third-generation  and  quarks, but with larger masses, are effectively excluded because of their impact on the Higgs boson production cross section. However, many models of new physics, such as those predicting a composite Higgs boson [1]}, [2]}, [3]}, [4]}, [5]}, or “little-Higgs” models [6]}, [7]}, include fourth-generation particles of a new type, called vector-like quarks (VLQs), labeled and B, having electric charges of \(+2e/3\)  and \(-1e/3\) , respectively. These VLQs do not obtain their mass via the Higgs boson Yukawa coupling, and will not affect the values of the Higgs boson production cross section or decay width. Therefore, these are viable search candidates for the LHC experiments, and are predicted to have masses at the scale [8]}, allowing the hierarchy problem to be resolved. We do not search for the related X and Y particles.
